Appending rig with constraints and drivers
I'm relative new to Blender rigging. I have successfully appended 2.81 generation custom character rig with many constraints and drivers into 2.93.
I made sure to rename/ make the rig as a collection in 2.8 Blender (which I haven't uninstalled). Like, Mary Rig Collection.
Then I append the (clearly named and easily identified) COLLECTION into 2.93.
Usually there's no drama, just need to disable/ hide custom bones. Drivers will work, constraints are all there.
After double-checking everything, I re-save a new 2.93 Rig Collection blend file of this character.
Good luck.